One of the most common problems in developing the proper golf swing is to prevent movement from a straight line position of the arm that provides control during the swing. In a right handed golfer, the left arm is the control arm. It is often difficult for a golfer during the swing to actually realize particular movement of the control arm during the swing since the golfer is concentrating on striking the ball. The present invention provides a lightweight, easily mounted indicating device which will inform the golfer (either audibly or visually) that the golfer's arm is not being maintained in a straight position during the swing if the arm should move. Further, the device is sized in volume and weight such that the device itself does not interfere with the golf stroke.